Atomic layer deposition (ALD) is recognized as a deposition technique that forms high quality materials with minimal defects and tight statistical process control. Even so, new deposition precursors and methods are sought that may be particularly suited to ALD. ALD of metal, metal oxide, and metal nitride films is typically accomplished with known organometallic precursors known as homoleptic compounds. Such compounds include a complex of a metal cation with multiple identical ligands. Common examples include Ti(NMe2)4, TiCl4, Hf(NMe2)4, HfCl4, WF6, and others, where Me represents CH3. Given the uniform chemical properties exhibited among the ligands of homoleptic compounds, the functionality of such precursors may be easily determined and matched with a desired deposition process.
A wide variety of heteroleptic compounds has recently been identified, such as in U.S. Pat. No. 6,632,279 issued to Ritala, U.S. Pat. No. 6,548,424 issued to Putkonen, and U.S. Pat. No. 6,552,209 issued to Lei. Such references, as well as others, identify numerous anionic and neutral ligands that may be used in organometallic precursors. However, given the large number of possible combinations of the numerous ligands and metal cations, truly myriad possible precursors have been identified. Little or no knowledge exists regarding any basis for selection of heteroleptic compounds as opposed to homoleptic compounds. Since different ligands exhibiting different chemical properties may exist in a heteroleptic compound, clearly the functionality of heteroleptic compounds cannot be easily matched to a desired deposition process, as is done with homoleptic compounds. Instead, differing and/or conflicting functionalities of heteroleptic compound ligands might introduce undesired deposited material defects and process complications into otherwise low defect, highly controllable ALD processes. Accordingly, a need exists for ALD methods matched to specified functionalities uniquely achievable with heteroleptic precursors.
Chemical vapor deposition (CVD) constitutes a well-developed technology, but further improvements continue to be made. Heteroleptic compounds may also have application in CVD methods and a desire exists to identify compounds that may be more advantageous in CVD compared to conventional homoleptic compounds.